György L. Balázs

Improved fire resistance by using Portland-pozzolana or Portland-fly ash cements

Our study was directed to the analysis of the influence of various types of cements on the behaviour of concrete at high temperatures. In our experiments binary blended and ordinary Portland cements were involved: two Portland cements with different clinker compositions and Portland cements containing pozzolanic additives as replacement of clinkers. In the first part of the study we focused on the influence of cement types where cement paste specimens were investigated. Then, based on the results of cement paste specimens, concretes specimens were prepared with some selected types of cements. Most important observation of our experimental study was that the pozzolanic additives and their increased amount have a favourable effect on the heat resistance (fire resistance) properties of concrete.

Modifications of material properties due to elevated temperatures

Recent fire cases in tunnels (Mont blanc, 20 March 1999, Gotthardt, 24 October 2001) and in highrise buildings (World Trade Center, 11 September 2001) indicated again the importance of fire research. Fast development of construction technology requires new materials. Initiation and development of fire are strongly influenced by the choice of construction materials [8]. In addition to their mechanical properties, their behaviour in elevated temperature is also of high importance [3].

Fire Resistance of Concretes with Blended Cements

An extensive experimental study has been carried out to analyse the post-heating characteristics of concrete subjected to high temperatures up to 800 °C. Major parameters of our study were the type and amount of supplementary cementitious materials (slag, fly ash, trass, silica fume, metakaolin) in cements and the level of maximum temperature (50, 150, 300, 500 or 800 °C). Present study includes analyses of surface cracking and residual compressive strength.

Concrete with Improved Chloride Binding and Chloride Resistivity by Blended Cements

Durability and service life of concrete structures can be endangered by chloride ions. Two phenomena help to keep control of chloride effects. On one hand cements are able to bind chloride ions by their aluminate clinker phases or by the clinker substituting materials. On the other hand resistivity of concrete against chloride penetration can be improved by careful selection of concrete constituents and production. Detailed results of two series of extensive experimental studies are presented herein. Chloride ion binding capacity of tested cements in decreasing sequence was the following: ( ) CEM III/B 32,5 N-S; ( ) CEM III/A 32,5 N; ( ) CEM II/B 32,5 R; ( ) CEM II/B-M (V-L) 32,5 R; ( ) CEM I 42,5 N. Test results indicated that the increasing substitution of clinkers by GGBS improves the chloride resistivity in concrete made with the same water to cement ratio. The application of air entraining agent increases considerably the values of . Based on the migration coefficients ( ) the following sequence of efficiency was found (from the best): CEM III/B 32,5 N > CEM V/A (S-V) 32,5 N > CEM III/A 32,5 N > CEM II/B-S 42,5 R > CEM II/A-S 42,5 N > CEM I 42,5 N.

Fibre Cocktail to Improve Fire Resistance

Favourable experience with fibre reinforced concrete (FRC) resulted in its increasing use worldwide. The properties of fibre reinforced concrete are mostly influenced by the type and the amount of fibres. Our experimental study was directed to the possible improvements of the residual flexural strength and the properties of concrete exposed to high temperatures with different fibre cocktails including steel, micro polymer or cellulose fibres. The influence of type and amount of fibres on residual flexural strength in cold state were tested after 300, 500 or 800 °C temperature loading.

Improved Fire Resistance by Using Different Types of Cements

Composition and microstructure of hardened cement paste have important influences on the properties of concrete exposed to high temperatures. An extensive experimental study was carried out to analyse the post-heating characteristics of concretes subjected to temperatures up to 800 °C. Major parameters of our study were the content of supplementary materials (slag, fly ash, trass) of cement (0, 16 or 25 m%) and the value of maximum temperature. Our results indicated that (i) the number and size of surface cracks as well as compressive strength decreased by the increasing content of supplementary materials of cements due to elevated temperature; (ii) the most intensive surface cracking was observed by using Portland cement without addition of supplementary materials. The increasing content of the supplementary material of cement increased the relative post-heating compressive strength. Tendencies of surface cracking and reduction of compressive strength were in agreement, i.e. the more surface cracks, the more strength reduction.

Material and Structural Properties for Creating High Performance Concrete Structures

HPC and UHPC concretes are finding their ways both to new structures and to retrofitting of existing structures. Herein specific material properties as well as structural examples are discussed. New Codes and Recommendations provide description of material properties and design rules for HPC/UHPC structures and structural elements.

Fibres in Concrete Structures

Fibres in concrete opened new ways of thinking in design and application of concrete as a structural material. Short fibres provide efficient ways to improve some specific properties of concrete members such as ductility, deformability, durability, as well as load bearing capacity. Parallelly bonded long fibres may form FRP reinforcements that can be applied internally like conventional prestressed or non-prestressed reinforcements. Otherwise they can be applied as externally bonded (EBR) or near surface mounted (NSM) reinforcements. Many applications show successful use. The present chapter intends to give an overview of the principal aspects of fibre-reinforced concrete, and on the other hand the main characteristics of EBR or NSM strengthening methods by using FRP. Specific details are given both on material and design aspects.